Create AccumulatingVelocityTrackerStrategy

This is a partial implementation of VelocityTrackerStrategy, that stores
data points during "add" operations. Extracting this logic into a common
class helps avoid duplicated logic across several strategies that do the
exact same thing when adding new movements. It also helps ease future
updates/optimizations.

Bug: 267211645
Test: atest libinput_tests
Change-Id: I116e978b070aa451813fefa384ccc65e10ea45a0